Method for microstructuring flat glass substrates

ABSTRACT

In the method for microstructuring flat glass substrates a substrate surface of a glass substrate is coated with at least one structured mask layer and subsequently exposed to a chemically reactive ion etching process (RIE) with at least one chemical etching gas. In order to provide the same or a higher quality etching and etching rate even for economical types of glass the chemical etching gas is mixed with at least one noble gas, so that the proportion of sputtering etching in the ion etching process is significantly increased.

CROSS-REFERENCE

This is a continuation of U.S. patent application Ser. No. 11/243,443,which was filed Oct. 4, 2005.

BACKGROUND OF THE INVENTION

1. The Field of the Invention

The present invention relates to a method for microstructuring glasssubstrates, especially flat glass substrates. A substrate surface of theglass substrate is coated with at least one structured mask layer andsubsequently exposed to a chemically reactive ion etching process (RIE)with at least one chemical etching gas.

Microstructures provided in glass change the optical properties of theglass. These microstructures are, among other things, required fordiffractive optical elements (DOE) and for micro-optical elements, forexample in projection and objective systems, in optical filters, in beamformation, as well as beam correction and color correction, but also influidics, in micro-reactors and other applications.

2. Related Art

In EP 0 644 462 B1 a method is disclosed, in which the v bn manufactureof microstructures on substrates by reactive ion beam etching (RIBE)takes place. In this method an ion source with an inlet tube for areactive gas or gas mixture and a cathode is used. Preferably afluorine-containing gaseous etching agent, for example CF₄ or CHF₃, isused. Also a mixture of reactive gas and inert gas can be used. Howeverthe components and the etching apparatus are exposed to high stresses orloads by reactive ion beam etching. Also the required structures cannotbe obtained with justifiable costs by this etching method.

DE 198 44 025 A1 describes different dry etching processes for workingoptical surfaces and for transferring optical structural elements tooptical materials for microstructuring quartz, quartz glass andquartz-containing surfaces. Also a reactive ion etching process(reactive ion etching, RIE) is described, in which CF₄, G₂F₆ or CHF₃ areused as principal components of the etching gas mixed with SF₆, XeF₂,NF₃ or CH₄, as well as an ion beam etching process for local surfaceworking. The ion energies should be greater than 600 eV, in order toguarantee a sufficiently high sputtering fraction in the etchingprocess. A disadvantageous increase in surface roughness can be avoidedby selection of the etching gas. However no etching rates, which aresufficient for current applications, may be obtained by the describedmethods for some preferred types of glass.

Ezz Eldin Metwalli and Carol G. Pantano, in “Nuclear Instruments andMethods” in Physics Research B 207 (2003), pp. 21-27 have described amethod of magnetically enhanced reactive ion etching, MERIE, ofsilicon-containing and phosphate-containing glass, on the one hand, in aCF₄/CHF₃-plasma and, on the other hand, for comparison purposes in anargon plasma. Especially it was found that the MERIE method can besuperior to conventional RIE regarding etching rate and that the etchingrate of glass in fluorocarbon plasmas decreases with increase ofchemically removable oxides in the glass. Silicate glass,boron-containing glass and glass with other components have asignificantly lower etching rate in comparison to phosphate-containingglass in pure argon plasma. The comparatively higher etching rate withphosphate-containing glass is based on the fact that the etchingmechanism is controlled by physical sputtering and thus thecomparatively low binding energy on the phosphate glass surface can beovercome. However these results do not apply to the use of CF₄ plasma.In that case the etching rate for quartz glass is clearly above theetching rate of other tested glasses. The cause for this is apparentlythat volatile SiF₄ was produced during chemical etching of SiO₂. Glasseswith ingredients, which produce non-volatile fluorides, have beenconsidered up to now as difficult or impossible to etch, among otherthings because of poor surface roughness.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method formicrostructuring flat glass substrates of the above-described kind, bywhich the above-described problems are overcome.

It is especially an object of the present invention to provide a methodfor microstructuring flat glass substrates of the above-described kind,which provides high quality structures with great structure depth withsmaller structure dimensions and with as high as possible an etchingrate.

It is an additional object of the present invention to provide a methodfor microstructuring flat glass substrates of the above-described kind,which is also provides good results with economical glasses, whichcurrently were considered to be unsuitable because of the poor chemicalsolubility of their ingredients for microstructuring in RIE processes.

This object and others which will be made more apparent hereinafter isattained in a method for microstructuring flat glass substrates, inwhich a substrate surface of a glass substrate is coated with at leastone structured mask layer and subsequently exposed to a chemicallyreactive ion etching process (RIE) with at least one chemical etchinggas.

According to the invention the chemical etching gas is mixed with atleast one noble gas, so that the proportion of sputtering etching in theion etching process is significantly increased.

Additional advantageous features are described and claimed in theappended dependent claims.

The dry etching method according to the invention by means of RIE formsmicrostructures on glass substrates, usually flat glass. The glass usedcan have a thickness of about 50 μm to up to 16 mm (BF 40 samples). Thesubstrate surface is first coated with at least one structured masklayer and subsequently chemically etched with a reactive ion etchingmethod with at least one chemically etching gas. Instead of an RIEmethod a MERIE method can also be used in the method of the invention,in which the RIE process is magnetically assisted. The ion etchingprocess differs from the state-of-the-art method because the chemicaletching gas is mixed with at least one noble gas, so that the proportionof the sputtering etching is increased significantly in the reactive ionetching method.

Thus the advantages of the chemical plasma etching, in which a chemicalreaction with the reaction gas occurs and volatile gases are formed, andphysical sputtering etching, in which atoms and clusters are released bymechanical impact by bombardment with ions, are combined especiallysignificantly with each other in unexpected ways. Ingredients, which arenot chemically released and remain, are released by physical sputtering.This leads, on the one hand, to high etching rates and, on the otherhand, to a more precise structure transfer with very small structuredimensions because of the anisotropic erosion due to sputtering.Furthermore a surface with reduced roughness, which scarcely differsfrom the roughness of the substrate glass, is produced. This RIE processdoes not significantly increase the surface roughness in comparison toan unetched glass surface. In contrast even improved roughness could beobserved. Also the surface roughness did not depend on the plasma powerused in the method.

It has been surprisingly established that a considerable increase of theetching rate results from the use of an etching gas mixture of at leastone etching gas and a noble gas in comparison to both a purely physicaletching and also a purely chemical etching. This increase of etchingrate may not be explained with the known models, according to whichglasses with a high silicon dioxide content have a higher etching ratethan those with a reduced SiO₂ content, and nearly the same etchingrates to multi-component flat glasses were found in purely physicaletching. Surprisingly especially good results are obtained for types ofglass, for which no good chemical etching results can be expected. Thisagain is based on the unexpected combination of physical and chemicalcomponents of the etching method.

In tests it has been shown that CF₄ is especially suitable as a chemicaletching gas and argon ions are especially suitable as sputtering gas.Especially the combination of both these gases leads to a high etchingrate. The method according to the invention is however not limited toboth these gasses. Furthermore mixing with other etching gases, forexample CHF₃, C₂F₆ and SF₆, and other sputtering gases (noble gases),for example Ne, Kr and Xe, has proven to be advantageous.

Furthermore in a surprising way varying the composition of the CF₄ andargon in the etching gas mixture maximizes the etching rate. In aparticularly preferred embodiment of the invention the CF₄ and argon arepresent in the etching gas mixture in a mixture ratio between 1:1 and6:1, preferably in a mixture ratio between 2:1 and 6:1, especiallypreferably in a mixture ratio between 2:1 and 4:1, and most preferablyin a mixture ratio of about 3:1, so that the CF₄ is the major portion ofthe etching gas mixture.

Different types of glass react very differently to a variation of thecomposition of the etching gas mixture (especially the variation of therelative amounts of CF₄ and argon) in the RIE method according to theinvention, as shown by use of the method. SiO₂ is rapidly chemicallyetched with CF₄ so that its chemical etching rate is comparativelylarge. Glass that contains aluminum, titanium, alkali oxides and otheringredients is comparatively more difficult to etch chemically. It hasbeen shown that especially the etching rate of these moredifficult-to-etch types of glass can be considerably increased(especially with increases in the proportion of the etching due tosputtering by argon ions). A comparatively high etching rate, which hasa pronounced maximum when etching gas mixture composition is varied, isobtained with flat glass containing SiO₂ and B₂O₃ in a sum total amountof from 60 to 90 (even 95) percent by weight, such as Schott Glass TypeBF 40 and AF 45. A very much smaller etching rate results with othertypes of Schott Glass, e.g. 8261, 8264, BF 33 and B270, under comparableconditions. The above-described maximum was not observable or wassubstantially weaker with these latter glass types. That means thatdifferent glass types react differently to the physical componentsduring etching erosion, namely to the accompanying argon ions. Thisbehavior is surprising and could not be expected from the results of thecomparative experiments. These comparative experiments were performed inan ion beam apparatus with an argon ion beam (purely physical erosion orremoval). The etching rate in these comparative experiments depends onlyweakly on the glass type.

It is known that silicon oxide glass may be satisfactorily etched.However this glass is difficult to produce and is expensive incomparison to multi-component glass. Furthermore wafer manufacture fromflat glass is simpler and more economical than with SiO₂ or other bulkglasses. A preferred embodiment provides that the method according tothe invention is performed with a multi-component glass, which containsat least three components. It has been shown that a series of thesemulti-component glasses have an etching rate behavior and structuretransfer precision comparable to that of silicon oxide glass, in so faras the method according to the invention is concerned. The RIE methodaccording to the invention thus allows economical starting materials tobe used without loosing etching quality and rate.

Suitable multi-component glass especially includes those with oxideingredients, which preferably contain SiO₂ and above all contain boronoxide, aluminum oxide and/or at least one alkali oxide. Borosilicateglass is most preferred. Economical boron-containing flat glasses ofSchott AG marketed under the trade names BF 40 [about 93% (SiO₂+B₂O₃)and 7% (Na₂O, K₂O, Al₂O₃)] and AF 45 [about 64% (SiO₂+B₂O₃) and 36%(BaO, Al₂O₃)] have especially good etching behavior. However it is alsopossible to apply the method according to the invention to glass that isnon-oxidic.

The dependence of etching rate for different types of glass on processgas pressure was measured for a pure CF₄ plasma and it was establishedin a surprising way that the optimum pressure is in a region from 30mtorr (about 4000 Pa) to 60 mtorr (about 8000 Pa). The etching ratedecreases with increasing process gas pressure above about 60 mtorr.This dependence is based on the fact that the ion etching method isalways a combination of chemical reaction (by reactive radicals of theetching gas) and physical erosion (by ion bombardment with plasma ions).At high pressure and thus inherently reduced bias voltage the physicaletching component is small, but at very low pressure sufficient reactiveradicals of etching gas are not available.

A preferred embodiment of the method according to the invention providesthat the substrate surface is coated with a metal layer and the metallayer is structured before performing the RIE and/or MERIE method. Achromium layer has proven especially satisfactory as the metal layer.The structured metal layer is used as a mask layer for the subsequentchemically reactive ion etching method according to the invention. Thechromium layer is especially suitable for this type of dry etchingprocess, since it is comparatively resistant to etching gas, such asCF₄, SF₄ or mixtures of these gases with e.g. argon. In contrast photoresist layers cover the substrate surfaces only about 10 min in etchingplasma with the above-described etching gas and are completely removedin this time period by the etching gas plasma. A shading or shadoweffect can easily occur with the thicker resist layers.

The metal and/or chromium coating occurs preferably using a magnetronsputtering method, by which suitable layer thickness is provided on thesubstrate, which are of the order of 150 nm.

The metal and/or chromium coating is likewise attacked during theetching process and at least partially etched away. In order to avoid oreliminate a process step comprising subsequent removal of the remainingmetal and/or chromium layer, in a further preferred embodiment of theinvention the thickness of the metal and/or chromium layer is selectedso that it is completely etched away during the etching process.

A photolithographic process for structuring the chromium layer is addedfollowing this coating process according to a further preferredembodiment of the method according to the invention. Here it is ofadvantage to coat a resist layer on the metal layer. Subsequently theresist layer can be illuminated with a mask and developed so that themetal layer is exposed on certain desired areas. Subsequently theexposed metal layer areas are removed by etching.

It has been advantageously established that the resist layer isstabilized when a soft-bake treatment occurs after application of theresist layer and/or a hard-bake treatment occurs after development ofthe resist layer.

The metal mask layers are removed by wet chemical methods, for examplewith sulfuric acid, after the ion etching method according to theinvention has been performed.

BRIEF DESCRIPTION OF THE DRAWING

The objects, features and advantages of the invention will now beillustrated in more detail with the aid of the following description ofthe preferred embodiments, with reference to the accompanying soleFIGURE, which is a schematic cross-sectional view of an apparatus formicrostructuring, which performs the method according to the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

A plasma reactor, in which a cathode 14 and an anode 16 are arrangedopposite to each other in a vacuum chamber 12, is shown in the FIGURE. Acooling device 18 cools the cathode 14

A sample 20, especially made of flat glass, rests on the cathode 14,which is subjected to microstructuring. A high frequency RF generator 22is provided, which produces high frequency electrical power, which iscoupled or introduced into the sample 20 by means of the cathode 14.Furthermore the RF generator 20 is connected with the anode 16.

The vacuum chamber 12 contains an inlet 24 and an outlet 26, throughwhich the respective gas mixtures enter and leave.

Experiments were performed with two flat glass samples made of SchottGlass BF 40 and Schott Glass AF 45 respectively, which acted assubstrates and had a size of about 50×50 mm². A surface of each flatglass substrate was coated with a chromium coating of 150 nm thick in amagnetron sputtering process. After that a photolithographic process forstructuring the chromium was performed.

In this photolithographic process first a resist AZ 5214 E(Manufacturer: Clariant) was spun on for 3 seconds at 1000 rpm and for40 seconds at 4000 rpm so that a resist thickness of 1.4 μm wasattained. The resist layer was subjected to a soft-bake process at 105°C. for 3 minutes. Subsequently the resist with a test mask in a maskaligner was illuminated with radiation at 25 mW/cm² for 5 sec. In orderto determine the minimal structure resolution, an electron beam writtenmask was used. The resist was then developed with a developer AZ 826 MIF(Manufacturer: Clariant), with a developing time of 40 sec. Subsequentlythe resist was subjected to a hard-bake process at 12000 for 5 min. Thenthe chromium layer was structured with chromium etch at 50° C. and withan etching time of 20 sec. The chromium-etch etching bath comprises 150g (NH₄)₂Ge(NO₃)₆ and 35 ml CH₃COOH (96%) in 1000 ml DL water.

The chromium layer structured in this way serves as a mask layer forsubsequent dry etching processes, which for example occurred in theabove-described plasma reactor with an HF plasma power of 300 W and aprocess gas pressure of 58 mtorr over a time period of 21 min.Experiments were performed with three different etching gas mixtures ofCF₄/Ar:

a. pure CF₄: CF₄ flow rate: 49 sccm

b. CF₄ Ar=3:1: CF₄ flow rate: 49 sccm, Ar flow rate: 17 sccm

c. CF₄:Ar=2.0:1: CF₄ flow rate: 49 sccm, Ar flow rate: 24.5 sccm

d. CF₄:Ar=1:1: CF₄ flow rate: 24 sccm, Ar flow rate: 24.5 sccm

It was shown that the gas composition had an influence on the resultingbias voltage. With the above-described process parameters a bias voltageof −540 V resulted with pure CF₄. Experiments were performed with amixture series of 1:1.2, 4:1, 2.9:1, 3.5:1 and 4.9:1 at a plasma powerof 300 W. The bias voltage was in the vicinity of −540 V.

The chromium mask layers were removed wet-chemically with sulfuric acidafter the etching process.

The tests in the plasma reactor were performed with an HF plasma powerof 300 W and a total flow rate of input operating gas between 49 and 66sccm. However for industrial applications considerably higher HF plasmapower (for example up to about 3000 W) and higher total flow rate values(for example up to 300 sccm) are recommended, in order to increase theetching rate.

The etched substrate surface was subjected to detailed observation witha microscope to determine the structure and with a mechanical surfaceprofile meter (Manufacturer: Dektak 3) to determine the etching depth,the profile course and the surface roughness in order to test thequality of the transfer of structure from the mask to the glass.

Increasing the physical component of the etching action by argon ions byvariation of the gas composition, acts differently on different types ofglass. This increase causes a greater removal of the chromium resistmask.

It was established by variation of the gas composition that the physicalcomponent of the etching action by bombardment of the surface with argonions had a significant influence on the etching rate, With a compositionCF₄:Ar=3:1 there is a considerable increase in etching rate, in fact2.5-fold increase, in comparison with pure CF₄. The maximum etching ratefor BF 40 was found to be in a range between 3.5:1 to 4.9:1. The etchingrate then falls off with further increasing argon fraction. However theetching rate is always higher than with pure CF₄ with a compositionCF₄:Ar=1:1 for Schott Glass BF 40.

The surface roughness in the case of plasmas in gas mixtures with someargon present was significantly different than with pure CF₄ plasmas,Very small structure dimensions of 1 to 2 μm could be obtained with theprocess according to the invention Etching depths of 600 nm could beobtained with etching times of about 20 min.

Experiments were performed, in which the process gas pressure was variedbetween 30 mtorr and 160 mtorr. It was shown that the bias voltagedepends on the selected process gas pressure and drops off withincreasing process gas pressure in the process according to theinvention. It was also shown that the optimal process gas pressure is ina range between 30 mtorr and 60 mtorr. The etching rate decreases withincreasing process gas pressure above about 60 mtorr.

The manufacture of electronic, especially of opto-electronic components,is an especially preferred embodiment for the microstructuring methodaccording to the invention. Suitable wafer packaging methods formanufacture of image chips are described in DE 102 22 960 A1. By thesemethods additional optical elements (for example micro lens arrays orDOEs) are embedded in cover glasses, whereby the electronic componentscan be formed so that they are compact and space-saving. The optics cancomprise an economical multi-component glass instead of quartz glass,silica or the like.

For example, at least one flat glass wafer and silicon wafer is used forthe manufacture in which the silicon wafer is structured and has anumber of sensor active and/or determining elements. The glass wafer isprovided with cavities (e.g. using wet-chemistry etching) at positionscorresponding to the elements of the silicon wafer. Additional opticalelements (such as micro lens arrays or diffractive optical elements) areprovided on the side of the cavities and/or on the opposite surface ofthe glass wafer at positions corresponding to the elements in thesilicon wafer by means of the microstructuring method according to theinvention. Both wafers are now bonded together and then isolated, sothat individual structural components, e.g. image chips, are produced.Since the optical elements on the glass wafer are applied to theelements of the silicon wafer before the isolating, only one adjustingstep per wafer pair is required. The cavities should guarantee asufficient spacing between the glass wafer surface and the elements ofthe silicon wafer. Also other suitable structure spacing or bondinglayers between both wafers can be added instead of the cavities.

The microstructuring method according to the invention has furtherapplications in the field of micro-optics, in which beam formation, beamdeflection or wavelength selection (filtering) can take place. Forexample the method can be used for optics for digital cameras or forlaser diodes. The specific optical structures that can be made by themicrostructuring method according to the invention are Bragg diffractiongratings, diffractive optical elements, phase holograms, microlenses(arrays) and Fresnel (zone) lenses.

The disclosure in German Patent Application 10 2004 049 233.6-45 of Oct.10, 2004 is incorporated here by reference. This German PatentApplication describes the invention described hereinabove and claimed inthe claims appended hereinbelow and provides the basis for a claim ofpriority for the instant invention under 35 U.S.C. 119.

While the invention has been illustrated and described as embodied in amethod of microstructuring flat glass substrates, it is not intended tobe limited to the details shown, since various modifications and changesmay be made without departing in any way from the spirit of the presentinvention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this invention.

1. A method for microstructuring flat multi-component glass substrates,said method comprising the steps of: a) coating a substrate surface of aflat glass substrate with at least one structured mask layer, said flatglass substrate consisting of a multi-component glass; b) mixing achemical etching gas with at least one noble gas in a mixture ratio ofthe chemical etching gas to the at least one noble gas of from 2:1 to6:1 in order to form an etching gas mixture; and c) performing achemically reactive ion etching process in which the substrate surfacecoated with the at least one structured mask layer is exposed to theetching gas mixture; wherein sputtering etching occurring in the ionetching process is significantly increased by the presence of the atleast one noble gas in the etching gas mixture but a major portion ofthe etching gas mixture consists of the chemical etching gas.
 2. Themethod as defined in claim 1, wherein the chemical etching gas used asreaction gas contains CF₄ or CHF₃ as principal component.
 3. The methodas defined in claim 1, wherein the at least one noble gas used assputtering gas comprises argon.
 4. The method as defined in claim 1,wherein the mixture ratio is from 2:1 to 4:1.
 5. The method as definedin claim 1, wherein the mixture ratio is about 3:1.
 6. The method asdefined in claim 1, wherein said multi-component glass contains at leastthree oxide ingredients.
 7. A method for microstructuring flatmulti-component glass substrates, said method comprising the steps of:a) coating a substrate surface of a flat glass substrate with at leastone structured mask layer, said flat glass substrate consisting of amulti-component glass; b) mixing a chemical etching gas with at leastone noble gas in a mixture ratio of the chemical etching gas to the atleast one noble gas of from 2:1 to 6:1 in order to form an etching gasmixture; and c) performing a chemically reactive ion etching process inwhich the substrate surface coated with the at least one structured masklayer is exposed to the etching gas mixture; wherein sputtering etchingoccurring in the ion etching process is significantly increased by thepresence of the at least one noble gas in the etching gas mixture but amajor portion of the etching gas mixture consists of the chemicaletching gas; and wherein the multi-component glass comprises boronoxide, aluminum oxide and at least one alkali oxide.
 8. A method formicrostructuring flat multi-component glass substrates, said methodcomprising the steps of: a) coating a substrate surface of a flat glasssubstrate with at least one structured mask layer, said flat glasssubstrate consisting of a multi-component glass; b) mixing a chemicaletching gas with at least one noble gas in a mixture ratio of thechemical etching gas to the at least one noble gas of from 2:1 to 6:1 inorder to form an etching gas mixture; and c) performing a chemicallyreactive ion etching process in which the substrate surface coated withthe at least one structured mask layer is exposed to the etching gasmixture; wherein sputtering etching occurring in the ion etching processis significantly increased by the presence of the at least one noble gasin the etching gas mixture but a major portion of the etching gasmixture consists of the chemical etching gas; and wherein saidmulti-component glass contains SiO₂ and B₂O₃ and a sum total of saidSiO₂ and said B₂O₃ present in the multi-component glass is from 60 to 95percent by weight.
 9. A method for microstructuring flat multi-componentglass substrates, said method comprising the steps of: a) coating asubstrate surface of a flat glass substrate with at least one structuredmask layer, said flat glass substrate consisting of a multi-componentglass; b) mixing a chemical etching gas with at least one noble gas in amixture ratio of the chemical etching gas to the at least one noble gasof from 2:1 to 6:1 in order to form an etching gas mixture; and c)performing a chemically reactive ion etching process in which thesubstrate surface coated with the at least one structured mask layer isexposed to the etching gas mixture; wherein sputtering etching occurringin the ion etching process is significantly increased by the presence ofthe at least one noble gas in the etching gas mixture but a majorportion of the etching gas mixture consists of the chemical etching gas;and wherein said multi-component glass contains Al₂O₃, B₂O₃ and/or TiO₂and a sum total of said Al₂O₃, said B₂O₃ and/or said TiO₂ present in themulti-component glass is from 5 to 40 percent by weight.
 10. The methodas defined in claim 1, wherein the chemically reactive ion etchingprocess is performed with a process gas pressure of 30 mtorr to 60mtorr.
 11. The method as defined in claim 1, wherein said substratesurface is coated with a metal layer and the metal layer is subjected toa structuring process.
 12. The method as defined in claim 11, whereinsaid metal layer is a chromium layer.
 13. The method as defined in claim11, wherein said metal layer is applied to the substrate surface using amagnetron sputtering process to coat said substrate surface with saidmetal layer.
 14. The method as defined in claim 11, wherein the metallayer has a thickness such that the metal layer is completely etchedaway in subsequent ion etching processes.
 15. The method as defined inclaim 11, wherein the metal layer is structured by a photolithographicprocess.
 16. The method as defined in claim 11, wherein a resist layeris applied to the metal layer, said resist layer is illuminated and thendeveloped and subsequently illuminated metal regions are etched away.17. The method as defined in claim 16, further comprising a soft-baketreatment after etching away the resist layer and/or a hard-baketreatment after developing the resist layer.
 18. The method as definedin claim 11, further comprising removing metal mask layer residue afterthe ion etching process by wet chemical methods.